Modulation On Magnetic Anisotropy In Inverse Perovskite Fe₄N

As a highly spin-polarized ferromagnetic material,Fe₄N has the advantages of high Curie temperature and low coercivity,which is important in spintronic devices.High storage density,low energy consumption and miniaturization are the goals of next generation spintronic devices,perpendicular magnetic anisotropy plays a key role in achieving these goals.In this dissertation,the perpendicular magnetic anisotropy of Fe₄N is expected to be realized by means of metal doping,molecular adsorption,oxide interface and magnetoelectric coupling effect.The main work is as follows:(1)The magnetic anisotropy of Fe₄N is tailored by doping 3d transition metals.It is found that the substitution at the face-center site decreases the crystal symmetry and enhances the magnetic anisotropy.Mn Fe₃N and Co Fe₃N have perpendicular magnetic anisotropy.Mn₃Fe N with cubic symmetry enhances the total magnetic moment and Ni₃Fe N has a large perpendicular magnetic anisotropy.Tetragonal crystal field splitting is the reason of the enhanced magnetic anisotropy in 3d metal doped Fe₄N.(2)In 4f rare-earth metal doped Fe₄N,the antiferromagnetic interaction appears between rare-earth atom and Fe atom.Pr Fe₃N and Nd Fe₃N with tetragonal structure exhibit a larger perpendicular and in-plane magnetic anisotropy,respectively.Spin-orbit coupling and tetragonal crystal field result in the enhancement of magnetic anisotropy,which provides a good guidance for finding new spintronic materials.(3)Perpendicular magnetic anisotropy of Co Fe₃N can be enhanced by adsorbing organic molecules C₆H₆,C₆F₆ and SC₄H₄,which can be ascribed to the formation of organic/ferromagnetic hybrid states.The electronegativity and symmetry of organic molecules will change the energy level of hybrid states,which can affect the magnetic anisotropy of Co Fe₃N.This finding will be benefit to design novel organic spintronic devices.(4)In Fe₄N/MgO heterostructures,the magnetic anisotropy can be modulated by metal doping,interfacial oxidation and external electric field.The contribution of magnetic anisotropy of Fe _I and Fe _II atoms in Fe₄N has the opposite responds to the external environment.Using the second-order perturbation theory,it is found that the change of magnetic anisotropy results from the redistribution of Fe d orbitals near Fermi level,which will promote the application of Fe₄N in spintronic devices.(5)In Fe₄N/PMN-PT heterostructures,the magnetic anisotropy can be tuned by ferroelectric polarization and interfacial oxidation.The interfacial magnetoelectric coupling leads to the spin splitting of Pb p orbitals,which induces the magnetic anisotropy of PMN-PT.The interfacial Pb atom has a crucial effect on the magnetic anisotropy of Fe₄N/PMN-PT heterostructures.These results provide a theoretical basis for electric-field-controlled perpendicular magnetic anisotropy in multiferroic heterostructures.